U.S. patent number 9,148,581 [Application Number 13/890,309] was granted by the patent office on 2015-09-29 for multi-function control illumination device.
This patent grant is currently assigned to National Chiao Tung University. The grantee listed for this patent is NATIONAL CHIAO TUNG UNIVERSITY. Invention is credited to Jen-Hui Chuang, Wen-Chih Teng.
United States Patent |
9,148,581 |
Chuang , et al. |
September 29, 2015 |
Multi-function control illumination device
Abstract
A multi-function control illumination device has a
synchronization separator, a parameter setting device, a light
emitting device, and a video processor. The synchronization
separator connects with a video camera and the parameter setting
device connecting with the light emitting device. The
synchronization separator receives a video signal from the video
camera, retrieves a synchronization signal from the video signal,
and outputs the synchronization signal to the parameter setting
device. The parameter setting device generates an electric signal
corresponding to the synchronization signal according to at least
one illumination parameter and outputs the electric signal to the
light emitting device. The light emitting device emits toward a
shooting direction of the video camera a light beam whose intensity
periodically varies according to the electric signal. Thereby, the
video camera captures images exposed by light beams of different
intensities lest nearby persons be overexposed and distant persons
be under-exposed.
Inventors: |
Chuang; Jen-Hui (Hsinchu,
TW), Teng; Wen-Chih (Hsinchu County, TW) |
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL CHIAO TUNG UNIVERSITY |
Hsinchu |
N/A |
TW |
|
|
Assignee: |
National Chiao Tung University
(Hsinchu, TW)
|
Family
ID: |
48547942 |
Appl.
No.: |
13/890,309 |
Filed: |
May 9, 2013 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20140198219 A1 |
Jul 17, 2014 |
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Foreign Application Priority Data
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Jan 15, 2013 [TW] |
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102101452 A |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N
5/2354 (20130101) |
Current International
Class: |
H04N
5/33 (20060101); H04N 5/235 (20060101) |
Field of
Search: |
;348/164,159,370,207.11,500,521 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Jonathan Dowdall, Ioannis Pavlidis, George Bebis; Face Detection in
the Near-IR Spectrum; Image and Vision Computing 21, Elsevier,
(2003), pp. 565-578. cited by applicant .
Peggy Joy Lu, Jen-Hui Chuang, Horng-Horng Lin; Intelligent
Nighttime Video Surveillance Using Multi-Intensity Infrared
Illuminator; Proceedings of the World Congress on Engineering and
Computer Science, 2011 vol. 1, WCECS 2011, Oct. 19-21, 2011, San
Francisco, USA. cited by applicant .
Yi-Ting Chen, Jen-Hui Chuang, Wen-Chin Teng, Horng-Horng Lin,
Hua-Tsung Chen; Robust License Plate Detection in Nighttime Scenes
Using Multiple Intensity IR-Illuminator; IEEE 2012, p. 893-898.
cited by applicant.
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Primary Examiner: Tran; Trang U
Attorney, Agent or Firm: Rosenberg, Klein & Lee
Claims
What is claimed is:
1. A multi-function control illumination device comprising: a
synchronization separator connecting with a video camera, receiving
a video signal from said video camera, and retrieving a
synchronization signal from said video signal; a parameter setting
device connecting with said synchronization separator, storing a
plurality of illumination parameters, receiving said
synchronization signal, and generating an electric signal
corresponding to said synchronization signal according to at least
one said illumination parameter; a light emitting device connecting
with said parameter setting device, receiving said electric signal,
and emitting a light beam with periodically-varying intensity to a
shooting direction of said video camera according to said electric
signal; and a video processor connecting with said video camera and
at least one display device, reordering said video signal, which
contains a sequence of frames respectively illuminated by different
light intensity within a period, and providing said frames
reordered for said display device by reordering said frames which
are illuminated by same level of light intensity to same display
sequence, and said frames with different illuminated light
intensity are reordered to the different display sequence.
2. The multi-function control illumination device according to
claim 1, wherein said light beam has N steps of intensities within
one said period, and wherein N is a natural number.
3. The multi-function control illumination device according to
claim 2, wherein said illumination parameters include a frequency
parameter, an intensity parameter, a step parameter, a pattern
parameter, a wavelength parameter, and a synchronization
parameter.
4. The multi-function control illumination device according to
claim 3, wherein said parameter setting device adjusts a length of
said period according to said frequency parameter.
5. The multi-function control illumination device according to
claim 3, wherein said parameter setting device adjusts intensity of
each said step independently according to said intensity
parameter.
6. The multi-function control illumination device according to
claim 3, wherein said parameter setting device adjusts a count of
said steps said intensities within one said period according to
said step parameter.
7. The multi-function control illumination device according to
claim 3, wherein said parameter setting device determines a pattern
of intensity variation within one said period according to said
pattern parameter, and wherein said pattern of said intensity
variation comprises a gradually-decreasing pattern, a
gradually-increasing pattern, a random pattern, an adaptive
max.-min. pattern, and so on.
8. The multi-function control illumination device according to
claim 3, wherein said parameter setting device determines that said
light beam is a single-waveband light beam or a dual-waveband light
beam according to said wavelength parameter.
9. The multi-function control illumination device according to
claim 3, wherein said parameter setting device controls said light
emitting device to emit said light beam during exposure intervals
of said video camera according to said synchronization
parameter.
10. The multi-function control illumination device according to
claim 1, wherein said electric signal is a voltage signal or a
current signal.
11. The multi-function control illumination device according to
claim 1, wherein said video signal is in an NTSC (National
Television System Committee) format or a PAL (Phase Alteration
Line) format.
12. The multi-function control illumination device according to
claim wherein said light emitting device is a dual-waveband light
emitting device.
13. The multi-function control illumination device according to
claim 1, wherein said light emitting device is an NIR (Near
Infrared) light beam generator or an SWIR (Short-wave infrared)
light beam generator.
14. The multi-function control illumination device according to
claim 1, wherein said parameter setting device further comprises a
memory storing said illumination parameters; a parameter generator
connecting with said memory, receiving said synchronization signal,
and obtaining at least one illumination parameter from said memory
to generate a parameter setting signal; and a control module
connecting with said parameter generator and said light emitting
device, receiving said parameter setting signal from said parameter
generator, and generating an electric signal corresponding to said
parameter setting signal.
15. The multi-function control illumination device according to
claim 14, wherein said memory is EEPROM (Electrically-Erasable
Programmable Read-Only Memory).
16. The multi-function control illumination device according to
claim 14, wherein said control module is a digital-to-analog
converter or a pulse width modulator.
17. The multi-function control illumination device according to
claim 14, further comprises a communication interface connecting
with said parameter generator and a computer, wherein said computer
controls said parameter generator through said communication
interface to set said illumination parameters in said memory.
18. The multi-function control illumination device according to
claim 17, wherein said communication interface is LAN (Local Area
Network) or UART (Universal Asynchronous Receiver/Transmitter).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination device,
particularly to a multi-function control illumination device.
2. Description of the Related Art
As the video camera has functions of image capturing and real time
monitoring, it has become an important tool for home security and
crime prevention. With advance of science and technology, the video
camera has been able to capture images in various environments,
such as indoors, inside transport vehicles, at night or in a rainy
day. Further, the video camera can also implement far-end
monitoring and assist in administration nowadays.
Daylight illumination is sufficient to make a video camera take a
clear image. However, the natural light source at nighttime is too
dim to make a video camera take an image. The current solution of
the problem is using an auxiliary infrared light source to assist
in taking images at night. As the conventional infrared light
source has a fixed intensity, the nearby persons are likely to
overexpose, and the distant persons are likely to underexpose.
Accordingly, the present invention proposes a multi-function
control illumination device, to overcome the abovementioned
exposure problem and provide additional functions to enhance image
quality.
SUMMARY OF THE INVENTION
The primary objective of the present invention is to provide a
multi-function control illumination device, which cooperates with a
video camera to undertake surveillance and video recording at
night, and which uses various combinations of a frequency
parameter, an intensity parameter, a step parameter, a pattern
parameter, a wavelength parameter and a synchronization parameter
to periodically emit light of pre-defined intensities to obtain
images of different exposures without detecting the light intensity
of the external environment. When the illumination device emits
more intense light, the illumination is more suitable to undertake
the surveillance and video recording of distant persons, preventing
from underexposure of the distant persons. When the illumination
device emits weaker light, the illumination is more suitable to
undertake the surveillance and video recording of nearby persons,
preventing from over-exposure of the nearby persons.
Another objective of the present invention is to provide a
multi-function control illumination device, which can achieve an
energy-saving effect via 3 techniques, (1) periodically vary the
intensity of illumination (not always the maximum light intensity),
(2) disable output during synchronization time and (3) PWM
techniques.
Yet another objective of the present invention is to provide a
multi-function control illumination device, which uses a
synchronization separator to extract the exposure timing of Video
camera. With the synchronized timing, a light illuminator can
synchronize the output of image of camera with the output of light
intensity of the illuminator, and wherein the synchronization speed
is dependent on the video frame rate. For example, the illumination
intensity varies per one-thirtieth seconds according to the NTSC
(National Television System Committee) standard.
A further objective of the present invention is to provide a
multi-function control illumination device, which alternately
generates two wavebands of infrared light beams, such as an SWIR
(Short-wave infrared) light beam and an NIR (Near Infrared) light
beam that are respectively reflected by a human face at different
reflectivity, to improve human face detection.
The last objective of the present invention is to provide a
multi-function control illumination device, which use a video
processor module to reorder/re-assign the sequence of images to
respective multiple display channels according to the level of the
intensity of light source, so as to improve the human viewing
problem arisen from the varying-intensity of image brightness.
To achieve the abovementioned objectives, the present invention
proposes a multi-function control illumination device, which
comprises a synchronization separator, a parameter setting device,
a light emitting device, and a video processor. The synchronization
separator connects with a video camera and receives video
information from the video camera. The synchronization separator
acquires a synchronization signal from the video information and
outputs the synchronization signal. The multi-function control
illumination device varies the illumination intensity according to
the timing of the synchronization signal to synchronize the
variation of the illumination with the exposure variation of the
video camera. The synchronization separator connects with a
parameter setting device, which stores a plurality of illumination
parameters, including frequency parameters, intensity parameters,
step parameters, pattern parameters, wavelength parameters, and
synchronization parameters. The parameter setting device receives
the synchronization signal and generates a corresponding electric
signal according to at least one illumination parameter. The
parameter setting device connects with the light emitting device.
The light emitting device receives the electric signal and projects
a single-waveband light beam or a dual-waveband light beam (such as
a light beam containing the SWIR beam and the NIR beam) to the
shooting direction of the video camera, wherein the intensity of
the light beam varies periodically. In order to solve the problem
that human beings are unsuitable to watch images exposed by a
sequence of different illumination intensities, the video processor
connects with the video camera and the display device, reordering
the images exposed by light beams of different illumination
intensities and providing the reordered images to the display
device.
Below, embodiments are described in detail in cooperation with
drawings to make easily understood the technical contents,
characteristics and accomplishments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram schematically showing the circuit of a
multi-function control illumination device according to one
embodiment of the present invention;
FIG. 2(a) schematically shows that the primitive sequence of frames
illuminated by different light intensities is unsuitable for human
viewing, wherein "steps" is arbitrarily set to 4 in this case, i.e
every 4 frames are illuminated by 4 respective different light
intensity periodically;
FIG. 2(b) schematically shows how to reorder frames which are
coming from primitive sequence of frames (shown as FIG. 2(a).)
illuminated by different light intensities, then display the
reordered frames of different group to respective display devices
(or display channels), wherein this procedure is illustrated by a
case which step is 4, and in reality, it cab be any natural
number;
FIG. 3 schematically shows a digital-to-analog converter and the
circuit of a light emitting device according to one embodiment of
the present invention;
FIG. 4 schematically shows a pulse width modulator and the circuit
of a light emitting device according to one embodiment of the
present invention;
FIG. 5 shows waveforms of intensity of light signals according to
one embodiment of the present invention;
FIG. 6(a) and FIG. 6(b) show the waveforms of different PWM-based
current signals according to one embodiment of the present
invention;
FIG. 7(a) and FIG. 7(b) show that the intensity variation waveforms
respectively have different frequencies according to one embodiment
of the present invention;
FIG. 8 shows an intensity variation waveform whose intensity on
each step can be adjusted respectively according to one embodiment
of the present invention;
FIG. 9(a) and FIG. 9(b) show that the intensity variation waveforms
respectively have different numbers of steps within a period
according to one embodiment of the present invention;
FIGS. 10(a)-10(g) show that the intensity variation waveforms
respectively have different patterns according to one embodiment of
the present invention;
FIG. 11 schematically shows a dual-waveband infrared light source
according to one embodiment of the present invention;
FIG. 12 shows the waveforms of image amplitude of a synchronization
signal and a corresponding light intensity according to one
embodiment of the present invention;
FIG. 13(a) shows the waveform of a light source having a constant
intensity according to one embodiment of the present invention;
FIG. 13(b) shows the waveform of an intensity-varying light source
according to one embodiment of the present invention; and
FIG. 14 schematically shows how to achieve the power-saving effect
by the blank time of a synchronization signal according to one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Below is introduced the principle of the present invention. The
multi-function control illumination device of the present invention
has 6 adjustable parameters, including parameters of frequency,
intensity, step, pattern, wavelength and synchronization, able to
periodically emit different pre-defined intensities of infrared
light beams. The CCD or CMOS video camera, cooperating with the
illumination device of the present invention, can obtain a sequence
of images respectively which are illuminated by different light
intensities. When the illumination device of the present invention
emits more intense light, the illumination is more suitable to
undertake the surveillance and video recording of distant persons,
preventing from underexposure of the distant persons. When the
illumination device of the present invention emits weaker light,
the illumination is more suitable to undertake the surveillance and
video recording of nearby persons, preventing from overexposure of
the nearby persons. With the periodically and sequentially changed
light intensities, the present invention can get as many as
intensities to meet as many as objects in the scene. Therefore, the
present invention can meet the requirement of exposure of
multi-object, which is very different from the prior-art that is
optimized for single object in the scene.
The multi-function control illumination device of the present
invention can operate in a constant intensity mode or a
periodically-varying intensity mode. Compared with the conventional
technology, the technology of the present invention, which
periodically varies the intensity of infrared LEDs, directly brings
forth an advantage: the illumination provided by the present
invention is more likely to expose both nearby persons and distant
persons adequately. The present invention is an open-loop
illumination device, operating independently without detecting the
brightness of the external environment. Contrarily, the close-loop
illumination device is a feedback-control system, which detects the
brightness of the external environment and then adjusts the
intensity of the light it emits according to the brightness of the
external environment.
Refer to FIG. 1 a block diagram schematically showing the circuit
of a multi-function control illumination device according to one
embodiment of the present invention. The multi-function control
illumination device 8 of the present invention comprises a
synchronization separator 10, a parameter setting device 14, a
light emitting device 16, and a video processor 22. The
synchronization separator 10 connects with a video camera 12. The
synchronization separator 10 receives a video signal in the NTSC or
PAL (Phase Alteration Line) format from the video camera 12,
retrieves a synchronization signal from the video signal, and
outputs the synchronization signal. The synchronization separator
10 also connects with the parameter setting device 14. The
parameter setting device 14 stores a plurality of illumination
parameters, including parameters of frequency, intensity, step,
pattern, wavelength and synchronization. The parameter setting
device 14 receives the synchronization signal and generates a
corresponding electric signal, such as a current signal or a
voltage signal, according to at least one illumination parameter.
The parameter setting device 14 connects with the light emitting
device 16, such as an infrared LED-based dual-band light emitting
device, an NIR generator or an SWIR generator. The light emitting
device 16 receives the electric signal and emits a light beam with
a periodically-varying intensity toward a shooting direction of the
video camera 12. Each period of the light beam has N steps of
intensities, and N is a natural number.
The parameter setting device 14 connects with a computer 20 through
a communication interface 18, and the computer 20 can set the
illumination parameters of the parameter setting device 14 through
the communication interface 18. In one embodiment, the
communication interface 18 is LAN (Local Area Network) or UART
(Universal Asynchronous Receiver/Transmitter).
The video camera 12 connects with the video processor 22, and the
video processor 22 further connects with at least one display
device 24. The abovementioned video signal includes a sequence of
frames respectively illuminated by different light intensities. The
light emitting device 16 provides light beams respectively having
different intensities for the video camera 12, whereby the video
camera 12 can capture images. However, human beings are unsuitable
to watch the image sequence exposed by the various light
intensities of illumination. Therefore, the video processor 22
distributes/reorder the frames illuminated by the same step of
light intensity to a new sequence of image group to corresponding
display channel. The image frames illuminated by a different step
of light intensity will be assigned/reordered to different sequence
of image group, then to a different display channel. The video
processor 22 reorders the frames of the video signal according to
the illumination intensities and provides the reordered frames for
the display device 24. Thus is solved the abovementioned problem.
Refer to FIG. 2(b), wherein four frame groups respectively
illuminated by four different light intensities are separately
presented on four blocks on an identical screen or four frame
groups respectively illuminated by four different light intensities
are separately feed to four display devices. The four light
intensities include the highest light intensity, the second highest
light intensity, the second weakest light intensity, and the
weakest light intensity. As shown in FIG. 1 and FIG. 2(a), the
video camera 12 assigns the primitive sequence of frames
illuminated by different light intensities to a single channel and
transmits the primitive sequence of frames to the video processor
22. If the primitive sequence of frames is presented on a single
screen, it would generate images suddenly dark, suddenly bright and
unsuitable for human vision. The present invention overcomes the
abovementioned problem via reordering the frames into different
groups according to the light intensities thereof and outputting
different groups of frames through different channels to present
them on different blocks of a screen.
The parameter setting device 14 includes a memory 26 (such as
EEEPROM (Electrically-Erasable Programmable Read-Only Memory))
storing a frequency parameter 261, an intensity parameter 262, a
step parameter 263, a pattern parameter 264, a wavelength parameter
265 and a synchronization parameter 266. The memory 26 connects
with a parameter generator 28. The parameter generator 28 receives
a synchronization signal and obtains at least one illumination
parameter to generate a parameter setting signal. The parameter
generator 28 connects with a control module 30, and the control
module 30 connects with the light emitting device 16, whereby the
parameter generator 28 connects with the light emitting device 16
through the control module 30. In one embodiment, the control
module 30 is a digital-to-analog converter or a pulse width
modulator. The control module 30 receives the parameter setting
signal from the parameter generator 28 and generates an electric
signal corresponding to the parameter setting signal. Refer to FIG.
3. If the control module 30 is a digital-to-analog converter 32,
the digital-to-analog converter 32 connects with the light emitting
device 16 containing a plurality of infrared LEDs 162 and generates
an analog current signal to drive the infrared LEDs 162 through a
resistor 33. Refer to FIG. 4. If the control module 30 is a pulse
width modulator 34, the pulse width modulator 34 connects with the
light emitting device 16 containing a plurality of infrared LEDs
162 and generates a PWM (Pulse Width Modulation)-based current
signal to drive the infrared LEDs 162. In one embodiment, the
abovementioned current signal has one of the waveforms shown in
FIG. 5, whereby the infrared LEDs 162 generate infrared light beams
whose intensities vary periodically.
In one embodiment, the PWM-based current signal has the waveform
shown in FIG. 6(a) or FIG. 6(b), wherein T.sub.H is the time
interval of the high-level signal, T.sub.L the time interval of the
low-level signal, and T.sub.H/(T.sub.H+T.sub.L) the duty cycle.
From FIG. 6(a) and FIG. 6(b), it is observed that the waveform of
FIG. 6(b) has a duty cycle larger than the waveform of FIG. 6(a).
The larger the duty cycle, the higher the average power, and the
brighter the light beams emitted by the infrared LEDs.
Below is introduced the operation of the present invention. Refer
to FIG. 1 again. Firstly, the synchronization separator 10 receives
a video signal from the video camera 12, retrieves a
synchronization signal from the video signal, and outputs the
synchronization signal to the parameter generator 28. Driven by the
synchronization signal, the parameter generator 28 obtains at least
one illumination parameter from the memory 26 and generates a
parameter setting signal according to the illumination parameter.
Next, the control module 30 receives the parameter setting signal
from the parameter generator 28, generates an electric signal
corresponding to the parameter setting signal, and outputs the
electric signal to the light emitting device 16. According to the
electric signal, the light emitting device 16 emits a light beam
with a periodically-varying intensity toward a shooting direction
of the video camera 12, whereby the video camera can capture
images. After a period of time, the abovementioned video signal
will contain a sequence of frames that were images of object
illuminated by different light intensities periodically. The video
processor 22 then further processes this kind of sequence of frames
by re-distributing the frames to different display channel (or
display device) for better viewing purpose. The video processor 22
can connect one or multiple display devices to display the
reordered images of different group. The algorithm that video
processor 22 adopts is that images exposed with the same level of
light intensity will be reordered to the respective display channel
(or display device). The display channel can be implemented by
hardware or software approach.
If necessary, the user can operate the computer 20 to control the
parameter generator 28 through the communication interface 18 to
set the illumination parameters in the memory 26.
Below are introduced 6 parameters of the multi-function control
illumination device of the present invention.
While the illumination parameter is the frequency parameter 261,
the parameter generator 28 and control module 30 of the parameter
setting device 14 adjusts the length of each period of the light
intensity variation of the light beam according to the frequency
parameter 261. The period of the light intensity variation of the
light beam can be adjusted arbitrarily within a given range with a
program to meet requirements of various nighttime monitoring tasks.
For example, FIG. 7(a) and FIG. 7(b) show 2 different frequency
settings, wherein FIG. 7(a)=15 Hz, and FIG. 7(b)=30 Hz.
While the illumination parameter is the intensity parameter 262,
the parameter generator 28 and control module 30 of the parameter
setting device 14 adjust the intensity of each step in a period
independently according to the intensity parameter 262 to enhance
the exposure quality of the nighttime images. If the intensities of
the steps cannot be adjusted independently, it is hard to achieve
that persons are all adequately exposed no matter where they are.
In the present invention, the intensity of each step can be
adjusted independently so that the light intensity in each step can
adequately expose the different persons at the different locations.
For example, there are 6 persons standing at distance 1 m, 2 m, 3
m, 5 m, 8 m and 15 m respectively from the CCD or CMOS video
camera. Everybody is exposed by light beams of 6 appropriate
intensities, as shown in FIG. 8. Thereby, the CCD or CMOS video
camera has the chance to obtain a better image for all the 6
persons since everyone is exposed at 6 different intensities. At
the best case, light intensity 1 is optimized for person 1, light
intensity 2 is optimized for person 2, light intensity 3 is
optimized for person 3, light intensity 4 is optimized for person
4, light intensity 5 is optimized for person 5, and light intensity
6 is optimized for person 6.
When all the steps are set to an identical intensity level (i.e the
illumination intensity does not change periodically, similar to
that of the conventional infrared illumination device.) Even under
such scenario, the present invention still outperforms the
conventional infrared illumination device because the present
invention can set the intensity to an arbitrary value but the
conventional infrared illumination device can only have a fixed
intensity (typically, it is "maximum"). Additionally, with
synchronization blank time, the present invention can save more
power than the traditional illuminator by disable output during
synchronization blank time.
If the pulse width modulator or digital-to-analog converter of the
present invention has a resolution of N levels, wherein N is a
natural number. then, there are as many as N light intensities can
be set to each step selection in the present invention.
While the illumination parameter is the step parameter 263, the
parameter generator 28 and control module 30 of the parameter
setting device 14 adjust the number of the steps in a period
according to the step parameter 263. For example, the variation is
set to 2 steps in a period (as shown in FIG. 9(a)) or 6 steps in a
period (as shown in FIG. 9(b)). The fewer the steps, the shorter
the period, and the less the imaging information. Fewer steps favor
fast scanning but impair enrichment of imaging information. The
more the steps, the longer the period, and the more plentiful the
imaging information. More steps favor enrichment of imaging
information but impair fast scanning.
While the illumination parameter is the pattern parameter 264, the
parameter generator 28 and control module 30 of the parameter
setting device 14 can select a pattern from a database of pattern
parameter 264 to meet its requirement for specific use case, such
as a gradually-increasing pattern (shown in FIG. 10(a)),
gradually-decreasing pattern (shown in FIG. 10(b)), a random
pattern (shown in FIG. 10(c)), an adaptive-max-min pattern (shown
in FIG. 10(d) and FIG. 10(e)), a geometrical-progression pattern
(shown in FIG. 10(f)), or an arithmetic-progression pattern (shown
in FIG. 10(g)). Each pattern can meets a specific use case
scenario. The geometrical-progression pattern can use fewer steps
to shift the illumination from bright to dark or from dark to
bright than the arithmetic-progression pattern. Therefore, the
geometrical-progression pattern has higher scanning efficiency than
arithmetic-progression pattern. The arithmetic-progression pattern
needs more steps to shift the illumination from bright to dark or
from dark to bright than the geometrical-progression pattern.
Therefore, the arithmetic-progression pattern has lower scanning
efficiency. The adaptive-max-min pattern with "the highest,
weakest, second highest, and second weakest light intensities
strategy" may have further higher scanning efficiency in nighttime
surveillance. The present invention can adopt different patterns to
meet different use cases and situations. The memory 26 can stores a
plurality of pattern parameter values (e.g. built in 64 patterns or
128 patterns . . . ) for various use case scenarios.
The parameter generator 28 and control module 30 of the parameter
setting device 14 also determine whether to adopt a single-waveband
infrared light beam or a dual-waveband infrared light beam
according to the wavelength parameter 265. In one embodiment, the
light emitting device 16 is realized by a dual-waveband infrared
light source containing an NIR light beam having a wavelength of
about 850 nm and an SWIR light beam having a wavelength of about
1450 nm. Refer to FIG. 11, wherein the hollow circlets represent
LEDs emitting light beams having a wavelength of 850 nm, and the
hatched circlets represent LEDs emitting light beams having a
wavelength of 1450 nm. The reasons to use the dual-waveband
infrared light source are that human skin has different
reflectivity to the 850 nm and 1450 nm infrared light beams and
that human faces or human skin can be detected more stably under
the illumination of the dual-waveband infrared light source. The
conventional infrared illumination device only uses a single
waveband infrared light beam and thus is unlikely to have the
advantage of a dual-waveband infrared light source: obtaining a
higher detection rate of images of human faces. In brief, the
present invention uses an NIR light beam having a wavelength of
such as 800 nm or 950 nm and an SWIR light beam having a wavelength
of such as 1450 nm. By using dual-waveband infrared light source,
the preset invention can get a higher detection rate of nighttime
human face detection.
The parameter generator 28 and control module 30 of the parameter
setting device 14 control the light emitting device 16 to emit
light reference to the timing of the output of exposed image of the
video camera 12, as shown in FIG. 12. The time interval between two
adjacent pulses of the synchronization signal is closely related to
the timing of the exposure of sensor of video camera 12. In the
synchronous mode, the intensity of the output light varies
synchronously (or with an offset) with some offset of the exposure
timing of the video camera 12. The synchronous mode can solve the
problem caused by asynchronization between the intensity variation
of the light emitting device 16 and the exposure activity of the
video camera 12 and thus makes easier the succeeding image
processing, such as the separation of the foreground and the
background or the image synthesis in HDR (High Dynamic Range) or
visual monitoring purpose.
The present illumination device can be operated both in
synchronization mode and asynchronous mode to meet different
application scenarios, whereby the present invention can work more
flexibly and powerfully. Typically, it will be used in synchronous
mode since camera can generate a sequence of more formatted images
under synchronous mode and achieve more power saving effect than
asynchronous mode. (will be explained in more details later). When
the synchronization parameter 266 are ser to "off", then the video
camera will operates in an asynchronous mode, which means the
timing of exposure in the CCD/CMOS sensor is independent to the
timing of the variation of intensity of light source. In such a
case, the intensity of the light emitted by the light emitting
device 16 does not vary with the images synchronously. So the
sequence of images got from asynchronous mode will be very hard to
be post processed due to the fact that the brightness of a sequence
of images will be unpredictable, and it's too complicated to
process this kind of sequence of images. However, the asynchronous
mode still has an advantage of lower price over synchronous mode
due to the cost of synchronization separator hardware can be save
in the asynchronous mode if our hardware are designed for low cost
scenario.
The computer 20 selects a pattern parameter value from the memory
26 via the communication interface 18 to satisfy the case required.
Alternatively, the computer 20 can select a pattern parameter value
from the memory 26 without using the communication interface
18.
Refer to FIG. 13(a). The illumination device of the present
invention can operate in a fixed intensity and consumes more power.
Refer to FIG. 13(b). Contrarily, the illumination device of the
present invention varies the intensity periodically and consumes
less power. Therefore, the present invention has a power-saving
effect. The actual ratio of the saved power is dependent on the
mode of intensity variation.
The reason is that the present invention enables the lighting of
the infrared light sources to synchronize with the synchronization
signal of the synchronization separator 10. Therefore, the
illumination device of the present invention does not emit light
during the blank time. If the blank time is 15% of the period, 15%
of power will be saved, as shown in FIG. 14. The present invention
has a very obvious power-saving effect because of the following
features: (1) the present invention adopts a PWM control
technology; (2) the illumination device does not emit light during
the blank time of the synchronization signal; (3) the intensity is
not fixed but varies periodically.
In conclusion, the present invention outputs light beams with
periodically-varying intensity to cooperate with the exposure of
the video camera by a sync separator design of the present
invention. The present invention thus simplifies the separation of
the foreground and the background and the HDR image synthesis by
synchronizing the timing of the varying-intensity of light source
and the exposure of video camera.
The embodiments described above are only to exemplify the present
invention but not to limit the scope of the present invention. Any
equivalent modification or variation according to the
characteristic or spirit of the present invention is to be also
included within the scope of the present invention. For example,
the present invention does not constrain that the light source must
be an infrared one although infrared light sources are used to
exemplify the light sources in the abovementioned
specification.
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